reserve T, X, Y for Subset of MC-wff;
reserve p, q, r, s for Element of MC-wff;

theorem
  (( (p => q) '&' p ) '&' s ) => q in IPC-Taut
proof
  set P = (p => q) '&' p;
A1: P => q in IPC-Taut by Th39;
  (P '&' s) => P in IPC-Taut by Def14;
  hence thesis by A1,Th26;
end;
